WO-A-95/03010 discloses a stent in the form of a metal tube having a long axis, a luminal surface and an abluminal surface, and a tube wall thickness, the tube carrying within the wall thickness a radiopaque marker made of a metal more radiopaque than the metal which forms the tube.
The stent of WO 95/03010 is created from a flat sheet of stainless steel material, by photochemical etching away of selected areas of the metal sheet, to leave behind an open lattice-work pattern, which is then rolled up into a tubular shape. A small round opening is provided at each end of the lattice area. Into each of these openings (called “eyelets”) can be pressed a radiopaque marker of material such as gold, platinum, tungsten or iridium. The markers are positioned in the eyelets by crimping.
EP-A-800 800 also addresses the problem of poor radiopacity of stents, but advocates a different solution. In a nickel titanium shape memory alloy stent, it is proposed to provide, at one end at least of the cylinder which defines the stent, at least one detection element which has the shape of a tongue extending substantially in the longitudinal direction of the stent, this detection element having a width, in the circumferential direction of the stent cylinder, which is greater than the characteristic width, in the circumferential direction of the stent, of each of the struts which make up the lattice work pattern of the stent. It is the greater circumferential width of the tongue which renders it more radiopaque than the thinner struts of the lattice of the stent.
EP-A-847733 Biotronik discloses a stent which is an apertured cylinder of titanium, to each end of which is welded a meander-form ring of tantalum. The radiopacity of tantalum being much greater than that of titanium, this construction allows the locations of the ends of the stent cylinder to be determined radioscopically.
WO-A-00/64375 ACS was published Nov. 2, 2000, that is, after the present priority date. It discloses a stent made from wire or tube but with end rings of a material more radiopaque that its lengthwise centre section. Materials suggested for the centre section comprise Ni--Ti shape memory alloy (Nitinol) and stainless steel. Materials suggested for the end rings comprise tantalum, platinum, gold and platinum-iridium. To attach the end rings to the centre section, it is suggested to use, inter alia, laser welding.
EP-A-709 068 Medinol discloses providing stent ends with “protrusions having enough metal therein to make them X-ray visible”. Gold and tantalum are mentioned as materials which are more visible under X-ray illumination than the stainless steel metal of the stent.
The disclosure of U.S. Pat. No. 6,022,374 is similar to that of WO-A-95/03010 mentioned above, in that it discloses an insert of radiopaque material within an eyelet formed in the stent. Mentioned as radiopaque materials are gold, platinum and alloys thereof.
DE-U-29904817 discloses a stent with axially extending projections at one end, at least. These projections can exhibit a thickening at their outer cantilevered ends. This concept can be compared with the disclosure of EP-A-800800, mentioned above.
U.S. Pat. No. 5,741,327 Frantzen discloses a stent with radiopaque markers attached to the ends of the body of the stent. In one embodiment, a circumferentially continuous serpentine marker element is attached to each end of the stent. This marker element can be of gold, silver, platinum or an alloy thereof It is disclosed that the body of the stent can be from a nickel-titanium alloy. The circumferential marker is radially expansible along with the body of the stent. A circumferential marker is attached to an end of the stent body using one of a number of techniques including brazing, mechanical fastening, weaving or epoxy adhesive. One specific system of attachment disclosed involves the use of “receivers” that extend from the ends of the stent body. These receivers are configured to receive “tabs” provided on the marker ring. Each tab has a neck and a knob at the end of the neck and the knob is received into a co-operating rounded space of the receiver of the stent body. A laser is used to achieve local melting so that the receiver and tab are fused together.
The disclosure of WO 97/33534 is similar to that of WO 95/03010, in that it includes radiopaque rivets set in a stent of less radiopaque material.